(CNN) – Leap day occurs every four years, adding an extra day to the end of February.
It keeps our calendar in alignment with the Earth’s revolutions around the sun.
Leap day has inspired traditions and superstitions.
In many European countries, any man who refuses a woman’s proposal must buy her 12 pairs of gloves.
People in Greece say that it’s unlucky to marry during a leap year, especially on leap day.
Leap day has played a role in pop culture, too.
The 2010 film “Leap Year” follows an American woman flying to Ireland to propose to her boyfriend on February 29.
There have even been a few leap day-themed TV shows, including a 2012 “30 Rock” episode that featured a character called “Leap Day William,” who emerges every four years to trade children’s tears for candy.